Participants in this observational study will report to the study site for an initial screening visit, followed by study visits every 6 months for at least 5 years. At each visit, participants will be interviewed and examined by a physician. Laboratory tests, including blood collection and a bone marrow aspirate, will also be performed. Data collected for this study's database will be used to determine the prevalence of clinical events and laboratory abnormalities over the course of disease, to study the evolution of disease parameters and symptoms, and to evaluate current therapies and diagnostic tests.